Since man first began a conscientious effort to heat the enclosures in which he works and lives, the storage of excess heat for use at a later time has been a problem. This not only applies to the storage of excess heat for disbursement between stokings of furnaces, stoves or the like to prevent roller coaster heat increments and decreases, but also on a much larger scale the storage of solar energy not only during night periods but also during extended cloudy days.
Although the collection of solar energy for heating purposes has been experimented with and known for a long period of time, it was only after the severe fossil fuel shortages of the mid-1970's that wide spread attention has been focused on the storage of excessive heat for later use over an extended period of time.
Although the problems of heat storage from combustion sources could be applied to the present invention, the greater storage volume involved in solar applications dicates that this area be more fully discussed. This is not intended however to in any way limit the application of the present invention to other heat storage applications.
In retrofit applications for existing structures, active solar applications generally are the most feasible. In these systems collector panels are mounted for maximum exposure to the sun and high temperature concentrated storage areas such as insulated hot water tanks, salts, drum storage areas, or the like are used therewith. These systems include forced heat transfer through liquid or gaseous mediums from the collecting means to the storage means and later from the storage means to the use application.
The various active solar systems, while being far superior to combustion heat sources as far as cost and availability goes, do require outside energy sources to move the heat transfer mediums and to otherwise effecuate control of the system.
For new construction, passive solar or quasi-passive solar systems have been developed in an effort to allow structures to be heated without active or forced heat transfer to and from the storage area or areas. The solar envelope or quasi-solar envelope wherein an outer shell is designed to retain heat in a sun space between such outer shell and an inner shell containing living or working space. These solar envelope structures generally include means for allowing the entrance of maximum sunlight during winter months for solar collection and minimum sun during the summer or warmer months of the year. This is done either through shade or louver means or by taking advantage of the variation of sun angles during different seasons.
In each passive solar application, the idea is to store a maximum amount of heat during sunlight hours which can be released during cloudy or night periods. Heat storage means for release during the non or low sunlight periods have taken various forms from water or liquid filled jugs and drums, to brick or stone lined areas, to small swimming pools, to sophisticated storage areas containing various types of minerals.
Each of the above heat storage systems has its own unique problems in either not adequately retaining the heat stored therein, requiring more volume than available space, or being cost prohibitive or a combination thereof.